1. Field of the Invention
The present invention relates to an on-demand type inkjet recording device, and particularly to a high-speed inkjet recording device that records images using a plurality of nozzles.
2. Description of Related Art
An inkjet recording device provided with a recording head having a plurality of nozzles can record images at a high rate of speed and at a high density on recording medium due to the plurality of nozzles.
Such inkjet recording devices are categorized as continuous type or on-demand type devices. The on-demand type inkjet recording device, such as that disclosed in Japanese unexamined patent application publication No. 2002-273890, has a simpler construction than that of the continuous system. Therefore it is possible to dispose hundreds or thousands of nozzles to be disposed at a high density in the on-demand type inkjet recording device.
However, in such a multi-nozzle inkjet recording device, the ejection velocity and weight of ink droplets ejected from multiple nozzles tend to vary widely among nozzles. When the ejection velocity varies, the position at which ink droplets land on the recording medium also varies, leading to an obvious deterioration in image quality in lines of text, figures, tables, and the like. When the weight of the ink droplets varies, on the other hand, the surface area of the dots on the recording medium also varies, producing irregular densities in the image, particularly halftone images.
Therefore, multi-nozzle inkjet recording devices have been proposed for regulating the ejection velocity or ink droplet weight for each nozzle by making separate fine adjustments to the drive voltage waveform applied to the piezoelectric element or heating element of each nozzle.
For example, Japanese unexamined patent application publication No. HEI-9-11457 provides a multi-nozzle inkjet recording device having a plurality of drive waveform generators for generating desired drive voltage waveforms. In this multi-nozzle inkjet recording device, appropriate drive voltage waveforms are selected for each nozzle to achieve a desired ink droplet weight or ejection velocity, and the selected drive voltage waveform is applied to the nozzle from the corresponding drive waveform generator.
Further, Japanese unexamined patent application publication No. HEI-4-316851 provides a multi-nozzle inkjet recording device having a single drive waveform generator capable of generating a plurality of drive voltage waveforms. In this multi-nozzle inkjet recording device, since the same drive voltage waveform is applied to all nozzles simultaneously, it is not possible to eject ink simultaneously from all nozzles while applying individual drive voltage waveforms to each nozzle. Therefore, a time-division method is used to apply an appropriate drive voltage waveform sequentially to one nozzle at a time, obtaining the desired ink droplet weight or ejection velocity.
However, in the conventional multi-nozzle inkjet recording device described above, including a combination of Japanese unexamined patent application publication No. HEI-9-11457 and No. HEI-4-316851, it is not possible to perform calibration for both ejection velocity and ink droplet weight simultaneously Variations in the weight can increase when variations in velocity are suppressed, while variations in the velocity can increase when variations in weight are suppressed.